1. Technical Field
The present invention relates to a terminal structure of a mounting structure suitably applicable to an electro-optical device.
2. Related Art
In the past, various electro-optical devices such as a liquid crystal display, an organic electroluminescence display, a plasma display, and a field emission display were known.
The liquid crystal display as an example of the electro-optical devices includes a liquid crystal display panel in which a liquid crystal layer is interposed between a pair of substrates and a flexible printed circuit (FPC) connected to the liquid crystal display panel. The liquid crystal display includes a mounting structure electrically connecting one substrate of the liquid crystal display panel and the FPC through terminals. The terminals in the mounting structure are supplied with predetermined potentials of signals through various lines. However, when a great potential difference exists between the adjacent terminals, the terminal having the higher potential may be corroded and broken due to an electrochemical reaction resulting from impurity ions included in the mounting structure, moisture permeated from the outside or the like, and an electric field. Therefore, in order to prevent the corrosion or break of the terminals or lines in the mounting structure, it is effective to exclude elements causing the electrochemical reaction as much as possible.
However, since the liquid crystal display including the mounting structure can be used under a high-temperature and high-humidity environment, it is difficult to completely remove the moisture from the mounting structure. Since the impurity ions are inherently included in the material of the mounting structure, it is also difficult to completely remove the impurity ions from the mounting structure. Therefore, by increasing a distance between the adjacent terminals having a great potential difference as greatly as possible in the mounting structure, it is possible to prevent the terminal of the two terminals having the higher potential from being corroded and broken due to the electrochemical reaction.
Regarding this technique, a flexible circuit board with high reliability in which signal supply lines are not corroded and broken due to the electrochemical reaction is described in JP-A-2001-332820. In the flexible circuit board, a linear dummy electrode not supplying a signal is formed between a power supply line and a reference potential line having a great potential difference of supply signals among the neighboring signal supply lines. Accordingly, since a strong electric field is not generated directly between the power supply line and the reference potential line, it is considered that the power supply line and the reference potential line should not be corroded and broken due to the electrochemical reaction with the impurities remaining in the flexible circuit board.
From the above-mentioned point of view, a circuit board capable of preventing lines from being corroded and broken due to electrical corrosion even when a difference exists in voltages applied to the adjacent lines is described in JP-A-11-142871. In the circuit board, plural lines are arranged in parallel on a substrate in an order of increasing potentials (decreasing potentials) applied thereto. Accordingly, since the potential difference between the adjacent lines is relatively small, it is considered that the line having the higher potential should hardly be corroded and broken due to the electrical corrosion. In the circuit board, since the potential difference between a ground voltage line and a gate-off level line is relatively great, the ground voltage line of both lines having the higher potential may be subjected to the electrical corrosion. Therefore, in the circuit board, by disposing a dummy line between both lines and supplying the higher potential of both lines to the dummy line, both lines are prevented from the electrical corrosion.
As described above, in order to prevent the terminals or lines from being corroded and broken due to the electrochemical reaction in the mounting structure, it is effective to increase the distance between the adjacent terminals when the potential difference between the adjacent terminals is great. However, even when the distance between the adjacent terminals having a great potential difference is increased, the terminal having the higher potential (particularly, terminal having a higher plus potential) is actually corroded and broken. Therefore, by using only these methods, it is not possible to completely prevent the corrosion and break of the terminals or lines due to the electrochemical reaction.
In JP-A-2001-332820 and JP-A-11-142871, in order to prevent the corrosion and break of the terminal having the higher potential between the adjacent lines, it is necessary to provide an independent dummy electrode to the flexible circuit board or the circuit board. Accordingly, in relations to other electronic components (for example, a driver IC), the layout of lines is complicated or the cost of product is increased.